Slip-enhanced plastic-damage constitutive model for masonry structures

Masonry structures are widespread in earthquake-prone areas. In this study, a slip-enhanced plastic-damage constitutive model is proposed for the nonlinear analysis of masonry structures, aiming to accurately and comprehensively predict the responses of masonry structures under strong earthquakes. Based on a framework of a bi-scalar plastic-damage model, a shear damage variable is introduced to describe the slipping failure of the bed joints. The tensile and compressive elastoplastic damage energy release rates are adopted as the driving forces of the tensile and compressive damage, respectively. The slip activation stress is proposed and adopted to drive the evolution of the shear damage. Then, to explore the damage and plastic evolutions, parallel systems of masonry under different uniaxial loading conditions are introduced, comprising a series of micro-elements with stochastic fracture strains. The macro stochastic damage evolution laws and plastic evolution law of the proposed model are determined based on the parallel systems. In addition, the procedures for parameter identification of the proposed model are discussed. An explicit numerical algorithm implementation is presented and integrated in finite element software ABAQUS. Finally, three numerical examples of unreinforced masonry walls with different height-width ratios under cyclic loading demonstrate that the proposed model can obtain reliable results that are in good agreement with test results, and several numerical examples of masonry panels with orthotropy illustrate that the proposed model has good extensibility.